The use of optical fibers in communication links has grown because of the high data rates achievable using optical communications. In addition, fiber optic links are less susceptible to electromagnetic interference and thus are used in military and other applications where the possibility of high levels of electromagnetic interference exists.
In general in optical fiber communications, fibers are designed to connect a transmission system and a receiving system with a minimum of optical losses. For long haul communication systems, the optical fiber communications link itself may include amplifiers at periodic distances for amplifying attenuated optical signals for the next leg of the long distance link. For relatively short optical fiber links, attenuation is generally less problematic. For certain short distance optical fiber applications, however, optical attenuation and predictable optical signals levels remain problematic.
Certain military applications, for example, utilize fiber optics to convey optical signals from a location that has good electromagnetic shielding to another location that does not have good electromagnetic shielding. As such, the optical fibers convey signals as light through a harsh environment, thus protecting the signals from electromagnetic interference. Such applications include optical fiber towed decoy applications. In these applications, decoys may be connected both physically and optically to an aircraft and one or more decoys may be towed behind the aircraft and deployed as a countermeasure to help the aircraft evade hostile, incoming guided missiles.
There are several problems associated with optical fiber towed decoys that are driven by the optical link performance. First, the optical loss between the transmitter and the optical receiver of the decoy is variable based on the number of connectors and the loss of each connector. Since the impact on the RF performance is 2:1 with respect to the optical connector and fiber losses, these losses are significant. Second, the optical loss can change as a function of time or the operating environment. In particular, fiber optic blind mate connectors that are exposed to the external environment can suffer degradation due to multiple mating cycles and a harsh environment in terms of cleanliness. With the current optical link design, there is not a way to compensate for the additional loss and system level RF performance may be negatively impacted. The current approach to addressing the optical loss variation is to maintain higher than desirable gain in the decoy. This high gain can be problematic because high gain in a small package can impact stability. Third, the current approach does not address compatibility between different platforms where the optical loss may be different. The current approach is based on a worst case loss allocation and the towed decoy gain requirements are higher than desirable to ensure system performance requirements are met. However, application of this system to other platforms is limited due to the worst case assumptions used.
There is a need, therefore, for a system and method of configuring a fiber optic system on an aircraft and on a towed decoy that are compatible across a wide range of optical attenuation in the optical fiber link. There is a further need for a method of producing an optical signal for driving a fiber optic towed decoy that is more robust, consistent and economical and to produce a signal level to the towed decoy that may be increased and adapted as conditions change. There is still a further need for a system and method that reduce or eliminate the impact of the platform optical loss on system performance while making the towed decoy more stable.